1. Field of the Invention
This invention generally relates to a guide bar for a chain saw, and more particular relates to a guide bar of which weight is lightened in order to promote the operation efficiency of a chain saw. The guide bar may be used for cutting wood, stone materials, concrete, etc.
2. Description of the Prior Art
Conventionally, this kind of a guide bar for a chain saw has been described in the Japanese Utility Model Laid-Open No. Sho-40-5277. The weight of this guide bar has been lightened by forming a number of through holes. Each of the through holes is filled up with such weight lightening members as synthetic resin, etc. so that it may not disturb the working operation due to that small twigs are inserted thereinto.
On the other hand, another guide bar has been also described in the Japanese Utility Model Laid-Open No. Sho-61-2901. This guide bar is lightened by forming shallow dents on the whole surface at both the sides thereof. Both the dents are also filled up with light materials as well as in the above guide bar.
But, if the diameter of the through holes is widened in order to sufficiently accomplish the lightening of the weight in the guide bar having through holes formed, of the above two types of guide bars, the strength and the rigidity of the guide bar may be lowered. As a result, the guide bar may be deflected in use and the working efficiency will be reduced. And the guide bar may vibrate in accompanying with the vibrations of the engine of a chain saw, thereby causing the cutting surface to be roughened. Furthermore, the weight lightening materials may come off due to vibrations in use and slight deflection of the guide bar. Therefore, the diameter of the through holes may be spontaneously restricted in order to prevent this kind of inconvenience, there may cause such a problem that the lightening of the weight of the guide bar can not be sufficiently accomplished.
On the other hand, as the thickness of the weight lightening material is very thin in a guide bar of which both the sides are provided with shallow dents, the weight lightening material may be warped in use. If the weight lightening material is warped, the edges of the weight lightening material come out from the side of the guide bar and may be caught at the cutting surface in use. Then, there may cause such a problem that the guide bar may not be used anymore.
In this kind of guide bar, the guide bar body 350 is provided with a dent 351 as shown in FIG. 66. By employing such a structure as have a filler material 353 like a shock-absorbing material, a weight-lightening material and an oil supplying material, etc., the weight of the whole chain saw can be accomplished together with achieving high performance of the whole chain saw. Thus, in order to secure the lightening of the weight and high performance of the whole chain saw as well as in the above, a guide bar shown in FIG. 69 is proposed. The guide bar body 350 is provided with through holes 352. A member in which two filler materials 353 are overlapped and fixed by a rivet 360 is inserted in every through hole 352.
In these conventional technologies, inversely tapered inserting portion 354a or protrusion 354b, etc. is provided on the inner circumferential portion of all the dents 351 or all the through holes 352. The outer circumferential portion of the filler material 353 is of such a shape that it can be fitted to the inserting portion 354 or the protrusion 354b, and a come-off preventing structure is employed therefor.
Hence, if the filler material 353 is increased in size, the filler material 353 may be floated or warped in the vicinity of the middle portion thereof as shown in FIG. 68 and FIG. 71 due to aging deformation or difference of thermal expansion between the filler material itself and the guide bar body. There may cause such a problem that the filler material may swell out from the side of the guide bar body 350. In this case, the contacting resistance with the cutting surface of wood may be produced, thereby causing the working efficiency to be remarkably spoiled. For this reason, only small filler materials may be used in the conventional guide bar and sufficient effects can not be expected in shock absorbing, lightening of the weight, oil supplying, etc.
This kind of inconvenience may occur when such a resin as have water sucking property is employed as filler material 353. Namely, the filler material 353 sucks in humidity or water from wood now under cutting or the ambient environments thereof and may swell out, and thereafter it may be dried and contracted. For this reason, in the case that there is no clearance between the guide bar body 350 and the filler material 353, such inconvenience as may be similar to the above may occur due to deformation of the filler material 353. To get rid of this kind of inconvenience, it may be considered that clearance between the guide bar body 350 and the filler material 353 may be secured in advance. However, in this case, as the outer edge portion of the filler material 353 can not be securely fixed to the guide bar body 350, the filler material 353 may be apt to come off from the guide bar body 350. And the aging deformation of the filler material 353 may occur very easily. As the aging deformation of the filler material 353 occurs, there may occur such a problem that the aging-deformed portion of the filler material 353 may be floated from the surface of the guide bar 350. In order to prevent this kind of inconvenience, it is necessary that such a filler material as have no water suction property or is not contracted when being solidified after filling is to be filled up so that any clearance between the filler material and the guide bar body may not be produced. However, such a filler material itself costs much and as the filling method thereof is difficult the cost therefor becomes high.
In the guide bar of the prior art shown in FIG. 67, the filler material 353 is cemented in the dent 351. However, even in this case, there may occur such a problem that the cementing portion of the filler material 353 may be easily peeled off due to vibrations produced by high speed travelling of the saw chain and oil and/or water which may enter the clearance between the dents 351 and the filler materials 353 in the working.
Furthermore, in the guide bar shown in FIG. 67, resin is filled up in the dents 351 by injection molding, thereby causing the filler material 353 to be formed. In this case, as resin may be slightly contracted in hardening, clearance may be produced between the dent 351 and the filler material 353 on completion, thereby causing the filler material 353 to be apt to come off.
Also, when a filler material 353 is filled up in the guide bar body 350, stage gap may be produced between the surface of the guide bar body 350 and the surface of the filler materials 353. If such a stage gap is produced, the working efficiency is spoiled in the working. Therefore, the stage gap has been conventionally eliminated by surface grinding or surface cutting. However, this work for surface grinding or surface cutting needs much cost, and it is not economical, too.